The Science & Technology
of Glass
Cambridge - Monday 4th to
Wednesday 6th September 2017



Adja Tore
<a.toure@lboro.ac.uk>

article posted 17 Apr 2017

Adja Touré graduated from the Chemistry, Physics and Electronics Engineering School of Lyon (France), specialising in chemistry and engineering process and from the University of Lyon where she undertook a masters degree in Engineering for Health and Medicine. She then started a PhD, working with Dr Jamieson K. Christie at Loughborough University, studying computer simulations of biomaterials for medical applications. Adja's research involves studying the influence of fluorine addition on the bioactivity of phosphate bioactive glasses.


Molecular dynamics simulation of phosphate based
bioactive glasses containing fluorine
A.B.R. Touré*, E. Mele, J.K. Christie
Department of Materials, Loughborough University,
Loughborough, LE11 3TU, UK


Phosphate-based bioactive glasses (PBGs) are used as biomaterials in many biomedical fields such as orthopaedics and dental surgery [1,2]. In addition to their bone cell growth and antigen expression enhancement properties [3], PBGs completely dissolve in an aqueous environment and the dissolution behaviour can be controlled by the glass composition and chemistry. In the biomedical field, this is an interesting property for drug or therapeutic metal ion release applications.

In this work, we aim at precisely describing the effect of integrating fluorine into the structure of PBGs. Since structural properties and bioactive behaviour are closely related, we will henceforth better understand the bioactivity of phosphate based glasses. This project focuses on the molecular dynamics simulation of the fluorinated phosphate-based bioactive glass (F- PBG) systems CaF2-P2O5-CaO. In a previous study [4], the structural changes associated with the addition of fluorine in the systems CaF2-P2O5-CaO-NaO were studied using ab initio molecular dynamics. The first effect observed was the oxygen replacement, in the PO4 tetrahedron, by a fluorine atom leading to a local decrease of network connectivity which is likely to increase the bioactivity. The possible presence of clusters of modifier-rich and network-rich regions which are likely to decrease bioactivity was considered insignificant due to the large amount of P-F bonding. The study concluded that the bioactivity was not substantially altered following the addition of fluorine.

We use classical molecular dynamics [5,6] to atomically model the structure of those fluorinated phosphate BGs on a larger length scale. To do so, we developed an empirical force field with ionic charges and the use of a shell model [7] for polarisation effects. The empirical fitting was performed by reproducing the structure of relevant bulk crystals: Ca5FO12P3, POF3, CaF2, PF5 with the Buckingham potential. The molecular dynamics simulations are performed on the following systems (P2O5) (50-x/2 ) - (CaO) (50-x/2) - (CaF2) (x) with x = 0, 5,10 and using the molecular dynamics code DL_POLY Classic. The amount of CaF2 is increased while the network connectivity is kept constant. Since the network connectivity of the glass is the main structural parameter affecting the bioactivity of the BGs, we are aim at simulating F-PBGs exhibiting similar bioactivities. In this talk, we present a full analysis of the structure of F-PBG, including the extent of any fluorine clustering.

References:

1. Abou Neel, E., Pickup, D. M., Valappil, S. P., Newport, R. J., and Knowles, J. C. (2009). Journal of Materials Chemistry, 19(6):690-701.
2. Salih, V., Franks, K., James, M., Hastings, G. W., Knowles, J. C., and Olsen, I. (2000). Journal of Materials Science: Materials in Medicine, 11(10):615-620.
3. Hoppe, A., Guldal, N. S., and Boccaccini, A. R. (2011). Biomaterials, 32(11):2757-2774
4. Christie, J.K., Ainsworth, R.I. & de Leeuw, N.H., 2014. Ab initio molecular dynamics simulations of structural changes associated with the incorporation of fluorine in bioactive phosphate glasses. Biomaterials, 35(24):6164-6171.
5. Allen, M. P. and D.J, (1987). Computer Simulation of Liquids. Clarendon Press
6. Frenkel, D. and Smit, B. (2002). Understanding Molecular Simulation: From Algorithms to Applications. Academic Press.
7. Dick, B. G. and Overhauser, A. W. (1958). Physical Review, 112(1):90-103.